This invention relates generally to photographic printing and specifically to a method and apparatus for the improving of print quality by blending or enhancement of small detail.
Photographic negatives frequently contain two problems which give rise to unsatisfactory appearance and difficulty in information retrieval from the final photographic print. One problem, graininess, is typified by the granular appearance of a print caused by enlargement to such a scale that the elements composing the gray background of the picture show up as distinct areas. This problem also appears in photographs of television pictures, caused by the horizontal scan lines of the television picture and in the halftone dots in newspaper photographs.
The second problem, lost detail, is one caused by the limited dynamic range of normal photographs in regard to contrast. This is apparent when high contrast between large areas of a photograph masks small detail which actually exists on the negative. This detail is not retrievable by normal printing methods because such printing methods result in very low local contrast in the extremely light and extremely dark areas. While methods exist to overcome these problems, all suffer from either the compromising of picture quality or from the need for complex and expensive equipment.
For instance, graininess may be removed by simple defocussing but excessive small detail is thereby lost. Also a conventional unsharp mask technique without a linear transmission filter may be used to reduce large scale contrast while retaining small detail, but this method gives up some exposure control accuracy and cannot blend small detail. Spatial filtering techniques may be used to accomplish both goals, to enhance or to blend details in prints, but they require highly accurate and expensive equipment and are complex to use. Spatial filters also limit the size negative which can be used and limit the overall image quality available.
The present invention makes available a simple, low cost method for both blending small detail and enhancing the contrast of details otherwise lost because of high contrast areas on the photograph.